WO 99/43706 discloses a number of mono- and double-acylated GLP-1 derivatives including some K18,26 and K18,34 derivatives.
WO 2011/080103 which published after the priority dates of the present application discloses a number of GLP-1 derivatives that are double-acylated at K26,37.
WO 06/097537 discloses a number of GLP-1 derivatives including semaglutide (Example 4), a mono-acylated GLP-1 derivative for once weekly administration which is under development by Novo Nordisk A/S.
Angewandte Chemie International Edition 2008, vol. 47, p. 3196-3201 reports the discovery and characterisation of a class of 4-(p-iodophenyl)butyric acid derivatives which purportedly display a stable noncovalent binding interaction with both mouse serum albumin (MSA) and human serum albumin (HSA).